Dual targeting antibody strategies are being applied to complex diseases where multifactorial modulation aims to improve therapeutic efficacy. CD20 is a non-glycosylated phosphoprotein expressed on the cell membranes of mature B cells. CD20 is considered a B cell tumor-associated antigen because it is expressed by more than 95% of B-cell non-Hodgkin lymphomas (NHLs) and other B-cell malignancies, but it is absent on precursor B-cells, dendritic cells and plasma cells. Methods for treating cancer by targeting CD20 are known in the art. For example, the chimeric anti-CD20 monoclonal antibody rituximab has been used or suggested for use in treating cancers such as NHL, chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL). Anti-CD20 antibodies are believed to kill CD20-expressing tumor cells by complement dependent cytotoxicity (CDC), antibody-dependent cell mediated cytotoxicity (ADCC) and/or induction of apoptosis and sensitization to chemotherapy, although some patients have been shown to develop resistance to or exhibit incomplete responses to anti-CD20 therapy (e.g., resistance to rituximab).
CD3 is a homodimeric or heterodimeric antigen expressed on T cells in association with the T cell receptor complex (TCR) and is required for T cell activation. Functional CD3 is formed from the dimeric association of two of four different chains: epsilon, zeta, delta and gamma. Bispecific antibodies that are capable of binding CD3 and a target antigen, such as CD20, have been proposed for therapeutic uses involving targeting T cell immune responses to tissues and cells expressing the target antigen.
A bispecific antibody having a CD20-binding arm and a CD3-binding arm may provide the necessary crosstalk to augment antitumor activity. A third modality in such a bispecific antibody is the Fc domain. Modification of Fc binding properties may further augment the antitumor potency of a therapeutic antibody.
Binding of an immunoglobulin Fc domain to its receptor results in a variety of signaling and immune responses. These various “effector functions”, such as CDC and ADCC, are the results of immunoglobulins of the G class (IgGs) forming a complex between the Fab domain of the IgG and a target antigen, whereas the Fc domain of the IgG binds to Fc receptors on effector cells. Some effector functions of IgG are independent of antigen binding and embody functions such as circulating serum levels and ability to transfer Ig across barriers. Other effector functions are considered essential for use in immunoglobulin therapies, such as cancer treatments. The ADCC mechanism in particular is considered to be one of the primary anti-tumor mechanisms of therapeutic antibodies already on the market such as rastuzumab (metastatic breast cancer) and rituximab (non-Hodgkin's lymphoma).
Current therapeutic strategies typically suggest that reduced effector functions (or reduced Fc gamma receptor binding) may be useful for antibodies whose aim is to neutralize or inhibit the biological activity of an antigen (e.g. antibody blockers or antagonists), or activate or initiate downstream cellular signalling (e.g. antibody agonists). However, the design of tumor targeting antibodies with reduced effector function is counterintuitive for tumor therapy, since it is expected that reduced cytotoxicity of target cells will not be efficacious to treat the disease, i.e. destroy tumor cells or inhibit tumor growth.
One strategy, described herein, utilizes differential Fc receptor binding combined with bispecific antigen binding to specifically target tumor markers as well as trigger tumor-specific T cell killing. The antibody's Fc domain is designed to carefully control Fc receptor binding to eliminate or reduce undesirable killing of cells like T cells, natural killer cells and macrophages bearing Fc receptors. A unique binding pattern with respect to Fc receptor interaction comprising FcγRII receptor binding interactions, but lacking FcγRI or FcγRIII interactions, has not been described in the art for a tumor-targeting Ig therapy.
Thus, the combination of bispecific B cell and T cell targeting antibodies with reduced binding to Fc receptors results in unexpectedly beneficial therapeutic properties. Bispecific antibodies that bind both CD3 and CD20 are especially useful in clinical settings in which specific CD20 targeting yet controlled and efficient cytotoxicity is desired.